Option 4 on the trainer, while it slowly regens your health like the trainer states, it also randomly shrinks your health bar, making it smaller than when you started. I've tested it a few times. Every time I use infinite health the health bar maximum will randomly get smaller until I'm being one shot by a monster.
I don't have that issue.
Have you tried this?:
Fist: collect health (normally on F1 and It is called "collect health"
Second: Activate "Max Health" (normally NumPad1)
Third: go into "Editor" and freeze the "Max Health" option.
If it still does not work:
Also freeze the "Health" option in the "player stats"-section (first option in the editor).
Freezing Max Health worked fine for me. so it should do that for you to - normally.